Chlorinated pyridine derivatives are known compounds and have been prepared by a number of processes. Such processes include, for example, those described in U.S. Pat. Nos. 3,420,833; 3,244,722; 3,732,230; 3,186,994; 3,538,100; British Pat. No. 957,276 and copending application No. 16,646 filed Mar. 1, 1979. The products of these processes have been used as herbicides and pesticides and as chemical intermediates in the preparation of other highly desired herbicide or pesticide products. Of the many chlorinated pyridine derivatives, 2,3-dichloro-5-trichloromethylpyridine is a particularly desirable intermediate for the prepartion of selective herbicides having wide utility in the presence of valuable crops.
In copending application Ser. No. 467,710 filed Feb. 25, 1983, 2,3-dichloro-5-trichloromethylpyridine is prepared in high yields and high purity by a process which comprises contacting 2-chloro-5-trichloromethylpyridine in the liquid state with chlorine in the presence of a catalyst at a temperature of 70.degree. to 250.degree. C., the improvement comprising employing an effective amount of catalyst selected from the group consisting of tungsten hexachloride, molybdenum pentachloride, tungsten oxytetrachloride, molybdenum oxytetrachloride and ruthenium chloride. The preferred catalysts are those containing tungsten or molybdenum.